<!DOCTYPE html>
<html lang="en">
<head>
	<meta charset="UTF-8">
	<title>Document</title>
	<style type="text/css">
		body{
			margin:0;
			padding:0;
		}
		.box{
			height: 500px;
			background: #aaa;
			position: relative;
		}
		.nav{
			width: 960px;
			height: 60px;
			background:#666;
			position: absolute;
			bottom:0;
			left:50%;
			margin-left:-480px;

		}
	</style>
</head>
<body>
	<div class="box">
		<div class="nav"></div>
	</div>

</body>
</html>